This invention relates to a steering system for a motor vehicle. More particularly, the invention relates to a rotary actuator assembly for an automotive strut steer-by-wire assembly.
Automotive steering systems which utilize a mechanical linkage arrangement to translate motion from the steering wheel within the vehicle to the road wheels in order to change the direction of the road wheels are well known in the art. Mechanical linkage systems may be hydraulically assisted to make it easier for the driver to steer the automobile. Mechanical systems are time tested and function well however they are expensive due to the large number of components required and they tend to be heavy because of the loads that are experienced during use. Moreover, hydraulic assist systems place an additional load on the engine of the automobile. Weight and load on an engine reduces fuel economy and available power. These are clearly undesirable.
In more recent times, hydraulic assist systems have been replaced by electric assist systems. This reduces both weight and engine load but these systems generally have maintained use of the mechanical linkages and so are still relatively expensive to build and still suffer from the weight of the linkages. In keeping with the persistent quest to increase fuel economy and profitability of automobiles it is desirable to further reduce componentry necessary to a reliable steering system for a motor vehicle.
The present invention is directed to a steering system which alleviates the drawbacks of the prior art by providing a reliable, cost effective and compact steering system which requires no mechanical linkage between the steering wheel of the vehicle and the road wheels of the vehicle. The foundation of the invention is a rotary actuator which is responsive to signals from an automobile steer-by-wire system. The rotary actuator system is configured to fit in a substantially nested relationship with a strut and coil spring assembly wherein the strut is attached to the chassis of a vehicle on one end and the wheel hub at the other end and the coil spring is bounded by a spring stop connected to the chassis proximate the strut attachment thereto on a first end and a spring seat attached to the strut on the other end. The rotary actuator comprises a motor attached to a first shaft which receives high speed output from the motor. The first shaft transfers the high speed motor output to a transmission which may be a gear assembly which transforms the high speed output of the motor to a low speed output. The low speed output is transferred from the gearbox to a second shaft. At least one torque rod is attached to the second shaft and transfers the low speed rotation through an arcuate slot in the spring seat to an annular member to which the torque rod is operably coupled, preferably on an outer diameter of the annular member. The annular member is attached on its inside diameter to the strut tube. The strut tube is directly connected to a road wheel. Generation of an arcuate movement of the torque rod by the motor, gear assembly and shafts causes the strut to rotate and thereby steers the road wheel to which that strut is connected. Preferably two rotary actuators are needed to steer a front-wheel-steer vehicle although it will be understood that if desired a single rotary actuator could be employed and mechanical linkage used to operate the opposite wheel. Moreover, three or four rotary actuators can be employed to operate a four wheel steer-by-wire system allowing all corners of the vehicle to be steered.